The calculation of these properties is done by a back-end server, specifically using the MolSync RPC calculation API. The app displays R/S and E/Z stereochemistry labels as a static overlay on the displayed structure. Tautomers, on the other hand, are interactive.
For the given structure, each of the possible tautomer transforms is indicated by a dotted outline around the affected atoms. Selecting/tapping the atom group applies the transform: the structure interconverts to the tautomer. The new tautomer has all of its possible transforms outlines, which means that tapping on various parts of the molecule allows the entire tautomer graph to be navigated.